The present invention is particularly applicable for use in connection with welding wire feeders and, therefore, the invention will be described with particular reference to wire feeders used in connection with a welding operation. However, the invention has broader applications and may be used with other types of wire or other wirelike materials.
It is, of course, well known that utilizing a welding wire as a consumable electrode in the welding process can enhance the weld. Furthermore, in order to maximize the appearance and strength of the weld, accurately controlling the feed of the welding wire is important. Another important aspect of utilizing a consumable welding wire is maintaining a consistent and reliable flow of wire to the welding operation. As can be appreciated, interruptions in the flow of the welding wire can stop the welding process thereby reducing its efficiency.
Another aspect of wire feeding relates to choosing the optimal welding wire for the particular welding process. In this respect, the type of metal to be welded and the desired strength properties of the welded joint, will dictate which welding wires should be utilized. As can be appreciated, different welding wires can have very different properties both metallurgically and physically. The primary concern in the invention of this application relates to the physical properties of the welding wire. There are several different types of welding wire including copper wire, steel wire and aluminum wire. Each of these wires have different physical characteristics which influence the drive unit of the wire feeder.
One such physical characteristic is the hardness of the wire which influences the pinch rollers ability to grip the wire and accurately control the feed rate of the welding wire. In view of the importance in maintaining a desired feed rate, the welding wire feeders known in the art include control systems to accurately control the rotation of the pinch rollers that drive the welding wire. But these control systems are effective only if the pinch rollers maintain a constant grip on the wire. More particularly, a set of pinch rollers are two opposing rollers having parallel but spaced roller axes. The rollers rotate in opposite directions about their respective axis such that the portions of the peripheral roller edges that face one another move in the same direction. The pinch rollers are moveable toward one another so the welding wire is sandwiched between both rollers. As the drive unit of the wire feeder rotates the set of pinch rollers, the engagement between the pinch rollers and the welding wire drives the wire in the desired feed direction. The feed rate of the wire corresponds to the surface speed of the peripheral edges of the pinch rollers. As can be appreciated, a wire feeder can include more than one set of pinch rollers as is shown in Seufer and one or all of the sets of pinch rollers can be drive rollers. It should also be appreciated that non-drive pinch rollers can be used to help direct the flow of welding wire.
Turning to roller grip, controlling the outflow of welding wire is a function of the accuracy of the step motor used to drive the pinch rollers and the slippage between the peripheral edges of the pinch rollers and the welding wire. As can be appreciated, if the pinch rollers move relative to the wire, namely, slide on the surface of the wire, the rotation of the pinch rollers is not fully translated into wire outflow. As a result, prior art welding wire feeders have utilized different peripheral surfaces on the pinch rollers to maintain accurate contact with the welding wire. These outer surfaces include knurling or even high friction materials on the surfaces of the rollers. But it is important that the contact between the pinch rollers and the welding wire does not damage the welding wire which can impact the wire outflow to the welding torch or gun and the welding operation. In addition, it is also advantageous to utilize pinch rollers that have a long service life to minimize the repairs necessary to maintain a properly functioning wire feeder.
It has been found that pinch rollers can be used in connection with different types of welding wires. However, the different physical characteristics of the many types of welding wire require different application forces to be applied by the pinch rollers against the welding wire. More particularly, a soft wire such as a copper wire, requires a low amount of application force to obtain the desired contact between the welding wire and the pinch rollers, In contrast, a steel wire requires a much greater application force to prevent slippage between the welding wire and the pinch rollers. In fact, the application force necessary to accurately move a steel wire would likely damage a copper wire. Other types of welding wire typically require different application forces. As a result of the different physical characteristics of the many welding wires, prior art feeders are set-up to only work in connection with only a small range of welding wires. Changing from a copper welding wire to a steel welding wire requires modifications to the wire feeder that often requires professional assistance.
A force generating device is used to create an application force that is transferred to the pinch rollers by a force applicator. The force generators can utilize a spring to produce the desired application force within a given range. As the spring is deflected, the application force increases. As is known in the art, a spring has a spring modulus or spring rate wherein the spring modulus is the additional force necessary to deflect the spring an additional unit distance. As an example, a compression spring having a 100 pounds per inch spring modulus will be compressed ½ inch by a 50 pound weight. Similarly, a spring cylinder having a spring with a 100 pounds per inch modulus will produce 50 pounds of force if the spring is compressed ½ inch. In connection with wire feeders, the 50 pounds force is used to create the application force on the welding wire.
The adjustability of the application force is at least in part a function of the force generator's ability to controllably compress the cylinder spring. As can be appreciated, based on the spring modulus which is linear, controllably compressing the spring will control the application force of the pinch rollers. Therefore it is important to be able to accurately control the compression of the spring. As is known in the art, threaded engagement between two components of the cylinder can be used to compress the spring and therefore control the application force. The accuracy of this arrangement is influenced by the gauge of threads used in the threaded engagement along with the spring modulus. As will be appreciated, a fine thread will provide finer adjustment ability than a coarse thread. Furthermore, a coarse thread will increase the amount of hand force necessary to compress the spring. But, the coarse thread will allow quicker changes to the application force.
One of the problems with prior art force generating devices is that ease of use must be compromised to provide increased adjustability to the application force. One such compromise is the use of a coarse threads to allowing quicker adjustment to the application forces for different welding wires.
Another problem with prior art force generating devices is that major modifications are necessary in order to obtain the application force necessary to work in connection with a wide range of wire types and wire sizes. The basis for the modifications is that force generating spring can produce only a limited range of forces. The range of forces needed to work in connection with both soft and hard wires is great enough to necessitate an excessively large spring cylinder and a significant amount of adjustment to change the application force from a desired force for a soft wire to a desired force for a hard wire. As a result, prior art wire feeders can require professional attention to change from one type of welding wire to another type of welding wire by necessitating changes to the force generator cylinder.
Yet another problem with prior art welding wire feeders is that the necessary adjustability for a soft wire is much different than the necessary adjustability for a harder wire. In this respect, in order to fine tune the application force for a soft wire, the force generating device must be capable of small incremental changes. More particularly, while a 10 pound change in application force will have a recognizable influence on the engagement between the pinch rollers and a soft wire, a 10 pound change in a harder wire may have virtually no recognizable change. Therefore, it is desirable to have finer adjustment abilities for softer wires. But, fine adjustment abilities can be a disadvantage with harder wires. The fine adjustment can increase the time and effort necessary to make the adjustment. In view of the fact that the threads utilized in the generator to compress the cylinder spring cannot be easily changed, a cylinder designed for fine adjustment of a soft wire may not even work with a hard wire. Conversely, a cylinder designed to be used in connection with a hard wire may not have the sensitivity necessary to make the fine adjustments for use in connection with a soft wire. These types of problems necessitate physical changes to the design of the wire feeder to change from a soft wire to a hard wire.